Asteroid resembling materials discovered in comet dust

Published: Friday, January 25, 2008, 11:50 [IST]

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Washington, Jan 25 : New research by scientists at Lawrence Livermore National Laboratory (LLNL) has revealed that the dust from the comet Wild 2 resembles asteroid materials rather than an ancient, unaltered comet.

"Wild 2 doesn't look like what we thought all comets should look like," said LLNL's Hope Ishii, lead author of the research.

This finding was made after latest analysis of the samples that Stardust mission returned to Earth in 2006, which also found out that in addition to containing material that formed very close to the young sun, the dust from Wild 2 is missing ingredients that would be expected in comet dust.

Though comets are expected to contain large amounts of the most primitive material in the solar system - a treasure trove of stardust from other stars and other ancient materials, in the case of Wild 2, that has not been found.

"The material found in primitive objects just wasn't there in the samples," said John Bradley, a LLNL author.

By comparing the Stardust samples to cometary interplanetary dust particles (CP IDPs), the research team found that two silicate materials normally found in cometary IDPs, together with other primitive materials including presolar stardust grains from other stars, have not been found in the abundances that might be expected in a Kuiper Belt comet like Wild 2.

This is one of the first studies to closely compare Stardust particles to CP IDPs. This class of IDPs is believed to contain the most primitive and unaltered fraction of the primordial material from which our planets and other solar system objects formed.

According to the research, the high-speed capture of the Stardust particles may be partially responsible for the team not finding comet-like materials from Wild 2 samples.

But, extra refractory components that formed in the inner solar nebula within a few astronomical units of the sun, indicate that the Stardust material resembles chondritic meteorites from the asteroid belt.

"The material is a lot less primitive and more altered than materials we have gathered through high altitude capture in our own stratosphere from a variety of comets," said Ishii.

"As a whole, the samples look more asteroidal than cometary," he added.